Aromatic hydrocarbons from lignocellulose biomass

ABSTRACT

Various embodiments of microwave-assisted systems, devices, and associated methods of operation are described herein. In one embodiment, a method for producing a bio-oil from a carbonaceous material includes feeding the carbonaceous material to a pyrolysis reactor, pyrolyzing the carbonaceous material in the reactor to produce a raw bio-oil containing oxidized aromatic hydrocarbons, and catalytically reducing at least a portion of the oxidized aromatic hydrocarbons in the raw bio-oil to produce an upgraded bio-oil having reduced aromatic hydrocarbons.

CROSS-REFERENCE TO RELATED APPLICATION(S)

This application is a non-provisional application of and claims priority to U.S. Provisional Application No. 61/938,416, filed on Feb. 11, 2014.

BACKGROUND

Ongoing research trend suggests that catalytic fast pyrolysis (“CFP”) as one promising approach to directly convert lignocellulose biomasses into gasoline range aromatic hydrocarbons (“AH”). A typical CFP process includes rapidly heating a solid biomass at high temperatures (e.g., greater than about 500° C.) to decompose the biomasses into a bio-oil. Subsequently, the bio-oil is subject to catalytic hydrocracking, for example, using zeolite-based catalysts, to be converted into aromatics, carbon monoxide (CO), hydrogen (H₂), carbon dioxide (CO₂), water (H₂O), and/or bio-char.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic block diagram of a pyrolysis system according to embodiments of the present technology.

FIG. 2 is a graph showing example compositions of bio-oils produced by a catalytic pyrolysis process according to embodiments of the present technology prior to and after catalytic upgrading at diverse reaction conditions.

FIG. 3 is a graph showing example compositions of bio-oils produced by a catalytic pyrolysis process according to embodiments of the present technology after catalytic upgrading at optimized reaction conditions.

FIG. 4 is a graph showing a flash point profile (solid line) of an example bio-oil that includes about 5% low flash point compounds (Toluene, Ethylbenzene, p-Xylene, and o-Xylene; flash point<38° C.), 10% medium flash point compounds (1-ethyl-3-methyl-Benzene, 1,3,5-trimethyl-Benzene, Indane, and 2-butenyl-Benzene; 38° C.<flash point<60° C.), and 85% high flash point compounds (2-ethenyl-1,4-dimethyl-Benzene, 1-methyl-1,2-propadienyl-Benzene, 1-methyl-1H-Indene, Naphthalene, 1-methyl-Naphthalene, 2-ethenyl-Naphthalene, etc.; flash point>60° C.). FIG. 4 also shows another flash point profile (dashed line) of the example bio-oil after compounds with flash points lower than 60° C. were removed by distillation.

FIG. 5 a shows a distillation profile (dash-dot line) of an example bio-oil inclusive of compounds with distillation points lower than 60° C., a distillation profile (solid line) of the example bio-oil exclusive of compounds with distillation points lower than 60° C., and a distillation profile (dashed line) No 2. D diesel fuel.

FIG. 5 b is a graph that shows carbon number distribution of an example bio-oil produced by a catalytic pyrolysis process according to embodiments of the present technology.

DETAILED DESCRIPTION

Various embodiments of microwave-assisted systems, devices, and associated methods of operation are described below. The term “pyrolysis” is used herein to refer to a thermochemical decomposition or transformation of an organic material (e.g., a lignocellulose biomass) at elevated temperatures in the absence of oxygen (O₂). The term “catalytic pyrolysis” refers to pyrolysis facilitated by a catalyst. Also, the term “biomass” generally refers to an organic source of renewable energy. Examples of biomass include wood (e.g., fir, pine, etc.), wood waste products (e.g. saw dust), agricultural products/wastes (e.g., wheat straws, corns, fruits, and vegetables, etc.). The term “raw bio-oil” generally refers to a bio-oil derived by direct pyrolysis without being undergone catalytic hydrocracking and/or other subsequent processing. In contrast, the term “upgraded bio-oil” generally refers to a bio-oil derived by catalytic hydrocracking and/or other suitable processing of a raw bio-oil. A person skilled in the relevant art will also understand that the technology may have additional embodiments, and that the technology may be practiced without several of the details of the embodiments described below with reference to FIGS. 1-5 b.

Conventional catalytic fast pyrolysis techniques suffer from certain limitations. For example, CFP processes typically have low rates of heat transfer to a biomass with large particle sizes. Thus, fine grinding of the biomass is typically required. Secondly, to the best knowledge of the inventor, controlling the formation of undesirable products (e.g., methane, aldehyde, acids, ketone, and carbon) during the rapid heating of the biomass has not yet been successful. Such formation may hamper the catalytic activity as the undesirable products can act as precursor(s) for coke formation. The formed coke may in turn block active sites on a catalyst.

Microwave-assisted pyrolysis (“MAP”) is one technique that can overcome certain disadvantages of conventional CFP processes. For example, MAP techniques can have significantly lower processing time and energy requirements than conventional CFP processes. In conventional CFP processes, heat is transferred from a surface of biomass towards the center by convection, conduction, and/or radiation. In contrast, microwave radiation can penetrate a material by transferring and converting electromagnetic energy directly into thermal energy. Thus, heat transfer via microwave radiation is more uniform throughout the volume of the material. Also, during microwave heating, the material is at higher temperatures than the surrounding space, which is directly opposite to convection heating. The lower temperatures in the surrounding space can also be useful in avoiding undesirable reactions and in condensing bio-oil products.

Without being bound by theory, it is believed that a raw bio-oil (sometime referred to as a “pyrolysis oil” or “bio-crude”) is a complex mixture of sugars, esters, furans, acids, ketones, alcohols, phenols, guaiacols, and other organic compositions. A raw bio-oil typically has a high oxygen content (e.g., 35-40%) and may be acidic, viscous, reactive, and thermally unstable. Thus, raw bio-oils typically cannot be directly used as a fuel or raw material in engines or traditional refineries. The high oxygen content may also lead to a low heating value of, for example, only 50% of a petroleum fuel. Thus, modification of raw bio-oils is needed in order to derive a usable fuel.

Catalytic cracking is one approach that can remove oxygen in the form of H₂O, CO, and/or CO₂ through de-oxygenation using, for example, zeolite as a catalyst. Such an approach may avoid hydrogen addition and may be operated at atmospheric pressures. A number of catalysts (e.g., HZSM-5, silicalite, H-mordenite, and H-Y and silica-alumina) may be used for catalytic cracking of raw bio-oils. During such catalytic cracking, a raw bio-oil has to be re-vaporized before catalytic conversion. However, a raw bio-oil typically cannot be completely vaporized once condensed. If heated to 100° C. or more, the raw bio-oil may rapidly react and produce a solid residue of around 50 wt % of the original bio-oil, and thus resulting in low yields. Accordingly, techniques for catalytic upgrading after pyrolysis and before condensation of raw bio-oils may be desirable to avoid or at least reduce the risk of the foregoing disadvantages.

Several embodiments of the present technology are related to systems, devices, and processes for pyrolysis (e.g., microwave-assisted pyrolysis) of a biomass coupled with a catalysis reactor using, for example, a zeolite catalyst or other suitable types of hydrocracking catalysts in the production of bio-oils. In particular, the inventor has recognized that by controlling a pyrolysis temperature during pyrolysis, a raw bio-oil with surprisingly high aromatic concentrations (e.g., in excess of about 40% (v/v)) and rich in oxidized aromatics (e.g. guiacol, phenolics, etc.) may be produced. Example pyrolysis temperature ranges include about 200° C. to about 300° C., about 300° C. to about 400° C., about 400° C. to about 500° C., and about 500° C. to about 600° C. As used herein, the term “oxidized aromatic” compound generally refers to a compound with a chemical structure having a benzene ring substituted by one or more nucleophilic groups (e.g. hydroxyl, methoxyl, etc.) at the ortho and/or para position. Examples of oxidized aromatic include phenol, guiacol, and cresol.

The inventor has recognized that by controlling the pyrolysis temperature and/or pyrolysis reaction time, formation of undesirable compounds in the raw bio-oil may be reduced or even eliminated while oxidized aromatic compounds may be enriched. Such undesirable compounds are believed to induce coke formation during hydrocracking (e.g., during the catalytic upgrade operation) or other further processing. Coking is one of the major challenges for bio-oil upgrading reactions. It is believed that re-polymerization of certain components of the raw bio-oil can lead to coking on a catalyst surface, and thus significantly reducing a number of active sites on the catalyst surface. For example, aldehydes can react with oxygenated aromatics to form coke. In another example, organic acids (e.g. acetic acid) in bio-oils may coke over the catalyst surface. Thus, by controlling the pyrolysis temperature and/or pyrolysis reaction time, aldehydes, organic acids, and other types of coke-producing compounds (collectively referred to as “coke precursors”) may be significantly reduced when compared to conventional techniques, resulting in low coke yields during the catalytic upgrade operation.

The inventor has also recognized that surprisingly high yields of aromatic hydrocarbons may be achieved by controlling the mass ratio of hydrocracking catalyst to biomass. Examples of hydrocracking catalyst to biomass ratio can be about 0.15:1; about 0.2:1; about 0.2.5:1; about 0.35:1; or about 0.5:1. As used herein, the term “reduced aromatic” compound generally refers to a compound with completely hydrogenated single or polycyclic aromatic rings. Examples of reduced aromatic compound include naphthalene and derivatives thereof, ethylbenzene and other benzene derivatives, p-xylene, or o-xylene.

As a result, by controlling at least one of the pyrolysis temperature, the pyrolysis reaction time, the catalysis temperature, or the mass ratio of hydrocracking catalyst to biomass, upgraded bio-oils with properties suitable as aromatic supplement for high octane fuels (e.g. marine and/or jet fuels) can be generated. Such upgraded bio-oils may be directly blended with a range of petroleum-based fuels. As used herein, the term “petroleum-based fuel” generally refers to a fossil fuel produced by fractional distillation of a crude oil at temperatures between, for example, about 200° C. to about 350° C. Examples of petroleum-derived diesel fuel may contain a mixture of hydrocarbons with carbon chain lengths between eight and twenty one.

The physical properties of upgraded bio-oils produced in accordance with embodiments of the present technology can be comparable to certain grades of fossil fuels, e.g. No. 2-D diesel fuel, Naval Distillate Fuels, F-76, Marine Gas Oil, Marine Diesel Fuels, Jet Fuel JP-5, MIL-T-5624M, and Military Diesel Fuel Marine (DFM). Examples of the physical properties can include a flash point, a distillation temperature, and a carbon distribution. In example bio-oils, the carbon distribution can be generally similar to F-76 and No. 2-D diesel fuels. The inventor has also recognized that removing C7 and/or C8 carbon compounds (e.g., through distillation) can improve the carbon distribution profile of the upgraded bio-oil. In one example, after distillation to remove low flash point benzene derives, the resulting upgraded bio-oil had a flash point of more than about 60° C.

FIG. 1 is a schematic block diagram of a pyrolysis system 100 according to embodiments of the present technology. As shown in FIG. 1, the pyrolysis system 100 includes an inert gas source 102, a reactor 104, a reactor heater 106, a catalytic converter 108, a condenser 112, and a separator 114 operatively coupled to one another. Though only the foregoing components are shown in FIG. 1, in other embodiments, the pyrolysis system 100 can also include valves, buffer tanks, and/or other suitable mechanical components. In further embodiments, the pyrolysis system 100 can also be configured to operate as a continuous process by incorporating, for example, a plug-flow reactor, a constantly stirred tank reactor, and/or other suitable processing units.

The inert gas source 102 can include a tank or other sources of nitrogen, argon, and/or other suitable inert gases. The reactor 104 can include a vessel constructed with a suitable material to contain a biomass 101 during pyrolysis. The reactor heater 106 can include a microwave heater, a radiant heater, a convection heater, and/or other suitable types of heat source.

The catalytic converter 108 can include a conversion chamber 110 and a heater/cooler 112 configured to maintain the conversion chamber 110 at a target temperature. In one embodiment, the conversion chamber 110 may include a packed bed of catalyst pellets (e.g., HZSM-5, silicalite, H-mordenite, silica-alumina, and a zeolite). In other embodiments, the conversion chamber 110 may include a substrate (not shown) carrying a catalyst. In further embodiments, the conversion chamber 110 may have other suitable components in any suitable arrangements.

In the illustrated embodiment, the condenser 112 includes a tube-and-shell heat exchanger. In other embodiments, the condenser 112 can also include plate-and-frame and/or other suitable type of heat exchanger. The condenser 112 may utilize any suitable coolant in a counter-flow, concurrent-flow, or other suitable arrangements. Example coolants can include cooling water, thermal oil, or cooling air. The separator 114 can include a flash tank or a vessel sufficiently sized and shaped to separate a condensate from the condenser 112 into syngas 116 and bio-oil 117.

The pyrolysis system 100 can also include one or more transmitters, gauges, and/or other instruments for measuring and/or transmitting one or more process variables to a controller 118. For example, as shown in FIG. 1, the pyrolysis system 100 can include an inert gas flow transmitter 122, a pyrolysis vapor flow transmitter 124, a reactor temperature transmitter 126, a converter temperature transmitter 128, a separator level transmitter 130, a syngas flow transmitter 132, and a bio-oil flow transmitter 134. In other examples, the pyrolysis system 100 may include additional and/or different instruments than those shown in FIG. 1. The controller 118 can include a desktop, laptop, and/or other suitable computing device having a computing processor and a memory containing instructions that can cause the computing processor to perform a control process as described in more detail below.

During operation, the inert gas source 102 supplies an inert gas as a continuous or intermittent flow to the reactor 104. The supplied inert gas generally completely displaces any oxygen in the reactor 104. The reactor heater 106 then heats and/or maintains the reactor 101 at a target pyrolysis temperature to cause the biomass 101 to undergo a pyrolysis reaction and produce a raw bio-oil as a vapor. It is believed that the raw bio-oil includes a mixture of sugars, esters, furans, acids, ketones, alcohols, phenols, guaiacols, and other organic compositions. As discussed above, the target pyrolysis temperature and/or pyrolysis reaction time may be controlled and/or otherwise adjusted based at least on a composition of the biomass 101, a moisture content of the biomass 101, and/or other suitable parameters to achieve a high oxidized aromatic content (e.g., at least about 40% v/v) while reducing or even eliminating coke precursors (e.g., aldehydes, organic oils, etc.).

The reactor 104 then supplies the raw bio-oil to the catalytic converter 108, which in turn converts the raw bio-oil to produce and/or increase a concentration of reduced aromatics or aromatic hydrocarbons (e.g. ethylbenzene, toluene, etc.) in the raw bio-oil, and thus producing a converted bio-oil. In one embodiment, the converter temperature, as measured by the converter temperature 128, can be adjusted to achieve a target level of aromatic hydrocarbon concentration in the converted bio-oil. For example, the controller 118 may be configured to adjust an output to the converter heater 112 to maintain the target converter temperature. In another embodiment, a flow rate of the raw bio-oil, as measured by the pyrolysis vapor flow transmitter 124, may be adjusted to achieve the target level of aromatic hydrocarbon concentration in the converted bio-oil based on a target ratio of raw bio-oil to catalyst. In other embodiments, the converter temperature, the flow rate of the raw bio-oil, and/or other suitable operating parameters may be adjusted to achieve the target level of aromatic hydrocarbon concentration in the converted bio-oil.

The condenser 112 then condenses the converted bio-oil, and the condensed bio-oil is separated in the separator 114. The light end of the non-condensed bio-oil is then withdrawn as the syngas 116, and the heavy end of the condensed bio-oil is then withdrawn as upgraded bio-oil. As discussed above, by adjusting and/or otherwise controlling at least one of the converter temperature or ratio of raw bio-oil to catalyst, upgraded bio-oils with high aromatic hydrocarbons suitable for direct blending with petroleum based fuels may be provided.

Experiments

Several experiments were conducted to investigate the effect of deoxygenation in catalyst reactor close coupled with pyrolysis of a biomass. In particular, direct catalytic cracking of a biomass pyrolysis vapor using a packed-bed catalysis close coupled with microwave pyrolysis was investigated to convert Douglas fir sawdust pellets to aromatics by a ZSM-5 Zeolite catalyst. The effects of catalysis temperature and catalyst to biomass ratio on the resulting bio-oil composition were examined. GC/MS analysis results showed that the bio-oil contained aromatic hydrocarbons with little or no oxygen. Aromatic hydrocarbons were enriched and become the most abundant compounds which were about 15% to about 92.6% in upgraded bio-oils under certain catalytic pyrolysis conditions. The aromatic hydrocarbons mainly included benzene, toluene, xylene, naphthalene, and derivatives thereof.

The effect of catalysis temperature on bio-oil chemical composition was analyzed with a fixed ratio of catalyst to biomass (0.25). The results show that the aromatic hydrocarbons were increased from 0.72% in raw bio-oil (no catalyst) to about 92.6% with a catalysis temperature of about 500° C. At a temperature of about 375° C., the aromatic hydrocarbon content was increased from 0.72% to about 78.1% with the increase of catalyst to biomass ratio from 0 to 0.39, as discussed in more detail below.

Materials.

The feedstock used was Douglas fir sawdust pellets (Bear Mountain Forest Products Inc., USA) which were approximately 5 mm in diameter and 20 mm in length with moisture content of 8%. ZSM-5 (Zeolyst International, USA; SiO₂/Al₂O₃ Mole Ratio: 50) was dried at 105° C. for 12 h and calcined at 550° C. for 5 hours.

Pyrolysis Apparatus

A pyrolysis apparatus generally similar to that shown in FIG. 1 was used for the pyrolysis tests. For example, a Sineo MAS-II batch microwave oven (Shanghai, China) with a rated power of 1000 W was used at the 700 W power setting. This power setting gave a heating rate of 100° C./min. 20 g Douglas fir pellets were placed in a 500 mL quartz flask inside of the microwave oven. The pyrolysis volatile vapor from the flask went through a packed bed catalysis reactor which was filled with catalysts; and then after the condensation system, the condensable liquid was collected as bio-oils. The non-condensable volatiles escaped as syngas at the end of the condensers where they were either burned or collected for analysis. The bio-char was left in the quartz flask. The weight of syngas was calculated using the following equation:

Weight of syngas=initial biomass mass−bio-oil mass−bio-char mass   (1)

Experimental Design

A central composite experimental design (CCD) was used to study the product yields (bio-oil and syngas). Two independent variables, catalyst to biomass ratio (X₁) and packed-bed temperature (X₂, ° C.) were chosen and are shown at various levels in Table 1 below. Yi was used as the dependent output variable. The reaction time was set as 9 minutes. The packed-bed catalytic reactor temperature was from about 268.9° C. to about 481.1° C. The catalyst to biomass ratio was chosen from 0.11 to 0.39 with a fixed loading of biomass (20 g).

TABLE 1 X₁: Catalyst to X₂: Packed-bed level biomass ratio temperature (° C.) −1 0.15 300  1 0.35 450 −r = −1.41 0.11 268.9 r = 1.41 0.39 481.1

For statistical calculations, the variables Xi was coded as xi according to Equation 2 below:

x _(i)=(X _(i) −X ₀)/ΔX   (2)

where x_(i) is the dimensionless value of the independent variable while X_(i) is the real value. X₀ is the real value of the variable at the center point and ΔX is the step length. A 22-factorial CCD, with 4 axial points (a=1.41) and 5 replications at the center points (n₀=5) leading to a total number of 13 experiments were used to study the reaction conditions. A second order polynomial equation (Equation 3) was used to describe the effect of independent variables in terms of linear, squared, and interaction. The predicted model for the response (Y_(i)) was:

$\begin{matrix} {Y_{i} = {b_{0} + {\sum\limits_{i = 1}^{2}{b_{i}X_{i}}} + {\sum\limits_{i = 1}^{2}{b_{ii}X_{i}^{2}}} + {\sum\limits_{i = 1}^{2}{\sum\limits_{j = {i + 1}}^{2}{b_{ij}X_{i}X_{j}}}} + ɛ}} & (3) \end{matrix}$

Where Y_(i) is the predicted response; b₀ is the interception coefficient, b_(i), b_(ii), and b_(ij) are coefficients of the linear, quadratic, and interaction effects; X_(i) is the independent variables; and ε is the random error. The statistical analysis of the model was performed by Design Expert 8 software. The coefficient of determination (R₂) and F test were used to determine the quality of fit of the second order equation. The effect of each independent variable and their interactions were determined. F test was used to determine the model parameter's significance (α=0.05).

Analysis of Bio-Oil and Syngas

The chemical compositions of bio-oils were determined using Agilent 7890A GC/MS (GC-MS; GC, Agilent 7890A; MS, Agilent 5975C) with a DB-5 capillary column. The GC was first maintained at 45° C. for 3 min and then increased at 10° C./min to 300° C. The injector temperature was 300° C. and the injection size was 1 μL. The flow rate of the carrier gas (helium) was 0.6 mL/min. The ion source temperature was 230° C. for the mass selective detector. The compounds were identified by comparing the spectral data with the NIST Mass Spectral library (Lei, et al., 2011). The water content of the bio-oils was determined by Karl Fischer Titrator (Mettler Toledo V30). The chemical compositions of syngas were determined by a Carle 400 gas chromatography (Chandler Engineering, Broken Arrow, Okla., USA) system with a thermal conductivity detector (TCD).

Results and Discussion

The experiment design and product yields are shown in Table 2 below. The bio-oil yields were from 32.20 to 37.75 wt %, while the syngas and bio-char yields were from 40 to 46.55 wt % and from 19.70 to 23.35 wt %, respectively. Comparing with conventional combined pyrolysis and cracking upgrading processes, from which a wide range of yields were resulted (28.45-40.83 wt % for bio-oil yields, 39.04 wt %-65.95 wt % for syngas yields, and 3.27-32.51 wt % for bio-char yields), the products yield variation of the experiments was in a smaller range because of mild pyrolysis conditions.

TABLE 2 Packed-bed Bio-oil Bio char Syngas Catalyst to Temperature yield yield yield Run Biomass Ratio (° C.) (wt %) (wt %) (wt %) 1 0.15 300 35.60 22.95 41.45 2 0.35 300 35.40 23.35 41.25 3 0.15 450 35.10 19.70 45.20 4 0.35 450 32.65 22.60 44.75 5 0.11 375 37.75 22.25 40.00 6 0.39 375 32.20 21.25 46.55 7 0.25 268.9 37.15 20.65 42.20 8 0.25 481.1 32.90 21.50 45.60 9 0.25 375 35.00 22.00 43.00 10 0.25 375 34.35 21.65 44.00 11 0.25 375 34.75 20.75 44.50 12 0.25 375 35.25 21.85 42.90 13 0.25 375 34.05 20.95 45.00

Equation (3) was reduced by using backward statistical analysis, and parameters were sequentially removed based on the coefficient's p-value until all remaining were significant (p<0.05). Using the results of the experiments, the first order equations were obtained showing the yields of bio-oil (Equation 4) and syngas (Equation 5) as a function of the catalyst to biomass ratio (Xi) and packed-bed catalytic reactor temperature (X₂, ° C.):

Y _(bio-oil)=43.85−13.12X1−0.02X2   (4)

Y _(syngas)=33.34+10.77X1+0.02X2   (5)

The P value of Equation 4 was 0.0005<α=0.05, and thus the linear model was believed to be significant to describe the bio-oil yield. The coefficient of determination (R₂) for Equation 4 was 0.78, which suggests that the model was finely representing the relationships among the independent variables. The model term b₀, X₁, and X₂ were significant because the P values for such model terms were 0.0005, 0.0011, 0.0027, respectively, all smaller than α=0.05.

The P value of Equation 5 was 0.0097<α=0.05, and thus the liner model was significant to describe the syngas yield. The coefficient of determination (R₂) for Equation 5 was 0.60, which suggests that the model was fairly representing the relationships among the independent variables. And the model term b₀, X₁, X₂ were significant because the P values for these model term were 0.0097, 0.046, and 0.0098, respectively, all smaller than α=0.05.

GC/MS Characterization of Bio-Oil

GC/MS was used to characterize the bio-oil chemical compounds which were categorized into ten functional groups, as shown in FIG. 2. Without catalysis, bio-oils from microwave pyrolysis of Douglas fir pellets were mixtures of acid, ketones, alcohols, phenols, guaiacols, furans, esters, and sugars. With catalysis close coupled with microwave pyrolysis, aromatic hydrocarbons not containing oxygen were enriched and became the most abundant compounds in the upgraded bio-oils. Aromatic hydrocarbons were about 15.4-86.5% in upgraded bio-oils under various catalytic pyrolysis conditions. Such aromatic hydrocarbons were mainly composed of benzene, toluene, xylene, naphthalene, and derivatives thereof. Phenols became the second abundant compounds which were from 8 to 39% with five main phenols: phenol, 2-methyl-phenol, 3-methyl-phenol, 2,4-dimethyl-phenol, and 3,4-dimethyl-phenol in bio-oils depending on reaction conditions. Guaiacols were significantly decreased by close coupled catalysis from 45% in raw bio-oils to 0-26% in upgraded bio-oils depending on reaction conditions. The guaiacols were mainly composed of 2-methoxy-phenol, 2-methoxy-4-methyl-phenol, 4-ethyl-2-methoxy-phenol.

Effect of Reaction Temperature

The effect of catalysis temperatures on chemical compositions of upgraded bio-oils was analyzed with a fixed ratio of catalyst to biomass (0.25) as shown in FIG. 3. The aromatic hydrocarbons were increased from about 0.72% in raw bio-oil to about 92.6% when the catalysis temperature was increased to about 500° C. Thus, the results showed that high temperatures favored the production of aromatic hydrocarbons. The phenols content was first increased from 5.5% in raw bio-oil to 39% at 375° C. then decreased to 5.9% when the temperature was increased to 500° C. The guaiacols content was decreased from 44.7% in raw bio-oil to 0% when the temperature was higher than 481° C. The furans content was decreased from 9.8% in raw bio-oil to around 1% when the catalysis temperature was higher than 375° C. The sugar content was decreased from 4 to 0% as the temperature was increased to more than 375° C.

Effect of Catalyst to Biomass Ratio

It was observed that when the catalysis temperature was fixed at 375° C., the aromatic hydrocarbon content was increased from 0.72% in raw bio-oil to 78.1% with the increase of catalyst to biomass ratio from about 0 to 0.39 (FIG. 4). The content of phenols was first increased from 5.5% (raw bio-oil) to 39.3% (catalyst to biomass ratio of 0.25) then decreased to 18.2% with the increase of catalyst to biomass ratio from 0 to 0.39. Thus, the results indicated that high ratios of catalyst to biomass favored aromatic hydrocarbons production as phenols were cracked to produce aromatic hydrocarbons. The guaiacols content was decreased from 44.7% in raw bio-oil to 0% when the catalyst to biomass ratio was increased to 0.39.

Mechanism Analysis for Close Coupled Catalysis Process

In this test, the highest aromatic hydrocarbon content (92.6%) was achieved when the catalysis temperature was about 500° C. and the ratio of catalyst to biomass was about 0.25. The content of acids, ketones, alcohols, phenols, guaiacols, furans, esters, sugars were 0.1%, 0%, 0.05%, 5.95%, 0%, 0.5%, 0%, and 0%, respectively in the upgraded bio-oil. Raw bio-oil produced by pyrolysis at 500° C. contained 0.71% aromatic hydrocarbons, 2% acid, 0.89% ketones, 1.5% alcohols, 5.46% phenols, 44.7% guaiacols, 9.8% furans, 2.51% ester, and 4.05% sugars. Thus, the aromatic hydrocarbons in the upgraded bio-oil were significantly increased while other compounds except phenols all decreased to about 0% when compared to the raw bio-oil.

The disappearance of these oxygenated compounds after catalysis was believed to be associated with dehydration, decarboxylation, and decarbonylation reactions. In particular, Douglas fir is a soft wood which contains about 21% hemicelluloses, about 44% cellulose, and about 32% lignin. In the close coupled catalysis with microwave pyrolysis of Douglas fir sawdust pellets, it is believed that furfural was first produced through the bond cleavage between O—C₅ and ring forming between C₂-C₅ positions of the main chain of xylan. Furans may then be formed from decarbonylation of furfurals. Cellulose was believed to decompose and dehydrate to form anhydrosugars such as levoglucosan and furans. Such furans may be first converted to intermediates (e.g., cyclohexene and 3,4-dimethylbenzaldehyde) and then transformed into aromatics, light olefins, and carbon oxides. It is further believed that lignin was primarily depolymerized and dehydrated to produce propenyl-guaiacols. Then phenols were generated from demethoxylation reactions of propenyl-guaiacols. The cleavage of O—CH₃ bond in guaiacols was indicated by the increased CH4 in the syngas observed by the GC analyzer and mainly contained H₂, CO₂, CO, CH₄, C₂H₄, and C₂H₆. Aromatic hydrocarbons such as toluene may then be obtained from catalyzed deoxygenation of phenols during catalysis.

From the foregoing, it will be appreciated that specific embodiments of the disclosure have been described herein for purposes of illustration, but that various modifications may be made without deviating from the disclosure. In addition, many of the elements of one embodiment may be combined with other embodiments in addition to or in lieu of the elements of the other embodiments. Accordingly, the technology is not limited except as by the appended claims. 

I/We claim:
 1. A method for producing a bio-oil from a carbonaceous material, the method comprising: feeding the carbonaceous material to a pyrolysis reactor; pyrolyzing the carbonaceous material in the reactor to produce a raw bio-oil containing oxidized aromatic hydrocarbons; and catalytically reducing at least a portion of the oxidized aromatic hydrocarbons in the raw bio-oil to produce an upgraded bio-oil having reduced aromatic hydrocarbons.
 2. The method of claim 1 wherein feeding the carbonaceous material includes feeding a carbonaceous material with a moisture content of about 0.5% to about 20% and a particle size from about 0.4 mm to about 5 mm.
 3. The method of claim 1 wherein pyrolyzing the carbonaceous material includes reducing formation of coke forming precursors.
 4. The method of claim 1 wherein pyrolyzing the carbonaceous material includes producing an aromatic carbon precursor rich pyrolytic product.
 5. The method of claim 4 wherein the precursor comprises at least one of guaiacol in an amount of about 30% to about 70%), phenol in an amount of about 4% to about 30%, furan in an amount of about 0.5% to about 10%, esters in an amount of about 0% to about 5%, or sugar in an amount of about 0% to about 15%.
 6. The method of claim 1 wherein pyrolyzing the carbonaceous material includes producing a syngas having about 10% to about 65% carbon monoxide, about 0% to about 7% methane, and about 0% to about 5% carbon dioxide.
 7. The method of claim 6 wherein catalytically reducing includes producing hydrogen in by inducing a gas shift reaction between carbon monoxide and water.
 8. The method of claim 1 wherein catalytically reducing includes catalytically reducing at least a portion of the oxidized aromatic hydrocarbons in the raw bio-oil in a vapor phase.
 9. The method of claim 1 wherein catalytically reducing includes producing an upgraded bio-oil containing at least one of benzene, toluene, p-xylene, o-xylene, indene, or naphthalene.
 10. The method of claim 1 wherein catalytically reducing includes producing an upgraded bio-oil having a flash point between about 128° C. to about 406° C.
 11. The method of claim 11 wherein catalytically reducing includes producing an upgraded bio-oil having a carbon number distribution in the range of C9 to C23.
 12. The method of claim 1 wherein catalytically reducing includes producing about 10% to about 40% upgraded bio-oil, about 10% to about 50% syngas, and about 10% to about 30% bio-char.
 13. The method of claim 12 wherein the syngas has a heating value of about 100 BTU/standard cubic feet to about 400 BTU/standard cubic feet.
 14. The method of claim 12 wherein the syngas has about 0% to about 25% hydrogen, about 0% to about 11% methane, and about 0% to about 37% carbon monoxide.
 15. The method of claim 1 wherein catalytically reducing includes catalytically reducing at least a portion of the oxidized aromatic hydrocarbons in the raw bio-oil to produce an upgraded bio-oil having reduced aromatic hydrocarbons at a temperature of about 100° C. to about 600° C.
 16. The method of claim 1 wherein catalytically reducing includes catalytically reducing at least a portion of the oxidized aromatic hydrocarbons in the raw bio-oil to produce an upgraded bio-oil having reduced aromatic hydrocarbons at a residence time of about 10 seconds to about 10 minutes.
 17. The method of claiml wherein carbonaceous material comprises lignin, hemicelluose, and/or cellulose.
 18. The method of claim 1 wherein catalytically reducing includes catalytically reducing at least a portion of the oxidized aromatic hydrocarbons in the raw bio-oil to produce an upgraded bio-oil having reduced aromatic hydrocarbons at a catalyst to carbonaceous material ratio of about 0.15:1; about 0.25:1; about 0.3:1; about 0.35:1; about 0.4:1; about 0.45:1; or about 0.5:1. 